Brushless motor drive device

ABSTRACT

The present invention relates to a drive device for a brushless motor utilizing no position detector for detecting the position of a movable element of the motor. 
     The drive device comprises a phase controlled loop for controlling an output of a voltage controlled oscillator (40) by supplying an electric power to motor driving coils (1, 2, 3), detecting the difference in phase between the power supply waveforms thereof and a counterrelectromotive force of the motor driving coils during a power supply interrupting period with the use of a phase difference detector (20) and inputting a detected phase difference signal to the voltage controlled oscillator (40), an oscillation frequency initializing means (70) and a driving transistor interrupting circuit (80).

FIELD OF TECHNOLOGY

The present invention relates to a brushless motor drive device whichdoes not make use of a position detector for detecting the position of amovable element of an electric motor.

BACKGROUND ART

As a means trend of improving motor durability and reliability, abrushless motor is being largely employed for various drive motors. Ingeneral, the brushless motor requires the use of a position detector fordetecting the position of a movable element. However, in order tofurther reduce the price and the size, a brushless motor which does notrequire the use of the position detector is necessary. A conventionalexample of a drive device for such a brushless motor is disclosed in,for example, the Japanese Laid-open Patent Publication No. 52-80415.

Hereinafter, the above described conventional drive device for thebrushless motor will be discussed with reference to the drawings.

FIG. 4 is a circuit diagram of the conventional brushless motor drivecircuit. In FIG. 4, driving coils 1 to 3 are connected at their one endwith each other. The driving coil 1 is connected at the other end to theanode of a diode 4, the cathode of a diode 5 and the respectivecollectors of driving transistors 10 and 13. The driving coil 2 isconnected at the other end to the anode of a diode 6, the cathode of adiode 7 and the respective collectors of driving transistors 11 and 14.The driving coil 3 is connected at the other end to the anode of a diode8, the cathode of a diode 9 and the respective collectors of drivingtransistors 12 and 15. The respective cathodes of the diodes 4, 6 and 8and the respective emitters of the driving transistors 10, 11 and 13 areconnected to a positive power supply line, and the respective anodes ofthe diodes 5, 7 and 9 and the respective emitters of the transistors 13,14 and 15 are connected to earth. The other ends of the driving coils 1to 3 are also connected with a filtering circuit 16 which generates anoutput to a power supply switching circuit 17. An output from the powersupply switching circuit 17 is supplied to the respective bases of thedriving transistors 10 to 15.

FIG. 5 is a diagram used to explain the operation of FIG. 4, wherein Uo,Vo and Wo represent respective waveforms of electric power signalssupplied to the driving coils 1, 2 and 3. The power supply waveforms Uo,Vo and Wo have their high harmonic components removed by the filteringcircuit 16 and are respectively converted by the filtering circuit 16into output signals F1, F2 and F3 which are delayed 90° in phase. It isto be noted that the filtering circuit 16 is a primary filter and isconstituted by, for example, a RC passive filter, a primary Millerintegrator, etc., the cut-off frequency of which is set to asufficiently low region as compared with the frequencies of the powersupply waveforms of the coils. The output signals F1, F2 and F3 areinputted to the power supply switching circuit 17. The power supplyswitching circuit 17 is constituted by a logic circuit and is adapted togenerate control signals U_(H), U_(L), V_(H), V_(L), W_(H) and W_(L) inresponse to the output signals F1, F2 and F3, respectively. Thesecontrol signals U_(H), U_(L), V_(H), V_(L), W_(H) and W_(L) are suppliedto the bases of the driving transistors 10 to 15 to cause the latter toperform respective switching operations. At this time, the switchingoperations are carried out so that a motor driving torque can generatein a constant direction at all times for driving a motor.

In the prior art construction, it is necessary to use the filteringcircuit having a cut-off frequency characteristic for each a phase ofthe driving coils and, accordingly, a number of capacitors of highcapacitance is required.

Also, where the inductance of the driving coils is high, the powersupply current to be passed through the coils tends to be delayed intime after the driving transistors are switched on and permanentmagnetic fields tends of be degaussed by magnetic fields generated bythe driving coils. A so-called an armature reaction exists. In such acase, it is well known that, when the driving coils are supplied with anelectric power in such timings as shown in FIG. 5, the efficiency tendsto be lowered. As a countermeasure, a technique in which the signals F1,F2 and F3 are somewhat advanced in phase to operate the drivingtransistors so as to compensate for a delay in power supply resultingfrom the armature reaction is disclosed in the Japanese Laid-open PatentPublication No. 62-80415, however, component parts such as capacitorsare further required to accomplish it. Also, the power supply waveformUo, Vo and Wo tend to be accompanied by spike noises generated when thedriving transistors are switched off, a variation in power sourcevoltage, a variation in current attributable to a change in load, and soon and therefore it is often difficult to obtain accurately a powersupply switching signal from the power supply waveform Uo, Vo and Wothrough the use of the filtering circuit. As a countermeasure, a systemhas been suggested such as disclosed in the Japanese Patent PublicationNo. 59-36519.

However, the system wherein the use is made of the filtering circuit forproviding the power supply switching signal from the power supplywaveform for the driving coils basically has the following problem. Inother words, a voltage drop resulting from both of the power suppliedduring the supply of the electric power to the driving coils andinternal impedances of the driving coils, a spike noise occurringimmediately after the interruption of the power supply, and so on tendto be superimposed on a fundamental wave (counterelectromotive force) ofthe power supply waveforms of the driving coils, which constantly varywith a variation in power source voltage and load. Accordingly, wherethe power supply waveforms of the driving coils are filtered to providethe power supply switching signal, an error tends to occur as a resultof the above described component which is superimposed on thefundamental wave (counterelectromotive force) of the power supplywaveforms while the latter constantly vary, and it is thereforedifficult to accurately supply the electric power to the driving coils.

In order to eliminate the above described conventional problems, variousmethods have been suggested to obtain the power supply switching signalaccurately, all of which are basically such that adjustment is effectedin the periphery of the filtering circuit for maintaining at a constantvalue the difference in phase between the driving coilcounterelectromotive force and the power supply switching signal, andthe adjustment is extremely cumbersome. Also, other than those necessaryfor the filtering circuit, a number of additional capacitors arerequired and, therefore, when the driving circuit is fabricated into anintegrated circuit, both of the number of component parts to beconnected and the number of connection pins tend to be increased,rendering the price high. Also, a system wherein no filtering circuit isemployed and, instead, the use is made of, for example, a microcomputerfor digitally providing the power supply switching signal is disclosedin the Japanese Laid-open Patent Publication No. 61-293191, which is tooexpensive.

As hereinbefore discussed, since the conventional drive device for thebrushless motor is so constructed that the filtering circuit is used toprocess the power supply waveforms of the driving coils to provide thepower supply switching signal having a predetermined phase relationshipto the position of the movable element, in which the switching signal isutilized to sequentially energize the driving coils, it is not possibleto obtain the accurate power supply switching signal because of avoltage drop in the driving coils resulting from the spike noisescontained in the power supply waveforms of the driving coils and theelectric current supplied, a variation of the superimposed componentresulting from the change of the power source voltage and the load, thearmature reaction and so on. Also, an increased number of capacitors ofhigh capacitance are required for constructing the filtering circuitand, in particular, when the driving circuit is to be fabricated in anintegrated circuit, both of the number of the component parts to beconnected and the number of the connection pins tend to be increased,rendering it to be disadvantageous in terms of price.

In view of the foregoing, a system such as disclosed in the JapanesePatent Publication No. 61-3193 is suggested wherein thecounterelectromotive force generated in the driving coils is shaped asto its waveform and the use is made of a phase locked loop (PLL) circuitto generate an appropriate phase pulse to permit the driving coils to besequentially supplied with the electric power to drive the motor.However, in such a system, a voltage drop resulting from the electriccurrent supplied during the supply of the electric power to the drivingcoils and the internal impedances of the driving coils, the spike noisesgenerated immediately after the interruption of the power supply and soon are superimposed and, therefore, it is extremely difficult to obtainthe pulse signal by shaping and arithmetically processing thecounterelectromotive force generated in the driving coils.

As hereinbefore discussed, the conventional drive devices for thebrushless motor have had the various problems.

Accordingly, the object of the present invention is to provide a drivedevice for a brushless motor wherein the necessity of the use of anumber of capacitors of high capacitance hitherto required in theconventional filtering circuit is eliminated and the sequential supplyof an electric power through the driving coils is possible without beingadversely affected by any possible effect brought about by spike noisescontained in the power supply waveform for the driving coils, avariation in power source voltage, a variation in load and an armaturereaction, wherefore a head loss of the driving transistors can beavoided to thereby to avoid any possible destruction of the drivingtransistors which would occur as a result of an increase of the heatloss.

Also, another object of the present invention is to provide a drivedevice for the brushless motor wherein the supply of an unnecessaryelectric power to the motor is avoided to minimize a loss.

DISCLOSURE OF THE INVENTION

The present invention is comprised of a plurality of phases of motordriving coils, a plurality of driving transistors connected with thedriving coils, a power supply switching signal generator forsequentially transmitting a power supply switching signal to the drivingtransistors for driving the drive coils, a voltage controlled oscillatorfor outputting a signal having an appropriate frequency to the powersupply switching signal generator, a phase difference detector fordetecting the difference in phase between a counterelectromotive force,generated in the driving coils during the interruption of the supply ofan electric power to the driving coils, and the power supply switchingsignals, a difference amplifier for amplifying an output from the phasedifference detector and for inputting it to the voltage controlledoscillator, an oscillation frequency initializing means for initializingthe oscillation frequency of the voltage controlled oscillator, and adriving transistor interrupting circuit for disabling the plural drivingtransistors and for starting the sequential supply of an electric powerto the driving transistors at the time the oscillation frequency isinitialized.

Accordingly, since it forms a feedback loop, that is, a phase controlledloop (PLL loop) by detecting the difference in phase between thecounterelectromotive force, generated in the motor driving coils, andthe power supply switching signal for the motor driving coils,controlling both of the frequency and the phase of the power supplyswitching signal in dependence on the phase difference detected andcausing the power supply switching signal to maintain a predeterminedphase relationship relative to the position of a movable element, thefiltering circuit hitherto used is rendered unnecessary and, therefore,all of various inconveniences resulting from the use of the filteringcircuit can be eliminated.

Also, since the difference in phase between the counterelectromotiveforce generated in the motor driving coils and the power supplyswitching signal for the motor driving coils is detected during theinterruption of the power supply, an accurate detection of the phasedifference is possible and the phase controlled loop can be stablyoperated.

In addition, immediately after the application of a power source voltageVcc, a constrained condition of the movable element as a result of acertain load during a normal rotation of the motor is detected in termsof the operation of the oscillation frequency initializing means and, bydisabling the plural driving transistors, an unnecessary power supply tothe motor during the constrained condition of the movable element isavoided and also any possible destruction of the driving transistors asa result of the head loss is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a drive device for a brushless motoraccording to one embodiment of the present invention;

FIGS. 2 and 3 are explanatory diagrams used to explain the principle ofoperation of FIG. 1;

FIG. 4 is a circuit diagram showing the conventional drive device forthe brushless motor; and

FIG. 5 is an explanatory diagram used to explain the operation of FIG.4.

BEST MODE OF CARRYING OUT THE INVENTION

Hereinafter, a drive device for the brushless motor in one embodiment ofthe present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a drive device for a brushless motoraccording to one embodiment of the present invention. In FIG. 1, likereference numerals are employed to denote like parts which are identicalin function with those of the conventional drive device for thebrushless motor and, therefore, the details thereof will not bedescribed.

In FIG. 1, the respective bases of the driving transistors 10 to 15 areconnected with outputs of a power amplifier 43 having inputs connectedwith respective outputs of a logic circuit 42. The logic circuit 42 andthe power amplifier 43 together constitute a power supply switchingsignal generator 44. The logic circuit 42 has an input connected with anoutput D1 of a frequency divider 41 having an input connected with anoutput of a voltage controlled oscillator 40. A phase differencedetection pulse generator 28, the frequency divider 41 and the powersupply switching signal generator 44 are connected so that anotheroutput D2 from the frequency divider 41 and the respective outputs U1,U2, V1, V2, W1 and W2 from the logic circuit 42 can be inputted to thephase difference detection pulse generator 28. The driving coils 1, 2and 3 are connected at one end with buffer circuits 21, 22 and 23 towhich associated signals having power supply waveforms Uo, Vo and Wo aresupplied. Respective output sides of the buffer circuits 21, 22 and 23are connected with a comparator 27 to which respective outputs U_(B),V_(B) and W_(B) from the buffer circuits 21, 22 and 23 are supplied, andare connected together at a common junction N_(B) through associatedresistors 24, 25 and 26, through which junction N_(B) is connected withthe comparator 27. An output PD from the comparator 27 is controlled byan output from the phase difference detection pulse generator 28. It isto be noted that the various component parts 21 to 28 togetherconstitute a phase difference detector 20 and that the output PD formsan output from the phase difference detector 20. An output side (outputPD) of the phase difference detector 20 is connected through a resistor32 with an inverting input terminal of an operational amplifier 31, andthe inverting input terminal and an output terminal of the operationalamplifier 31 are connected together through a series circuit of resistor33 and capacitor 34 and a capacitor 35. A non-inverting input terminalof the operational amplifier 31 is applied with a predetermined biasvoltage through resistors 36 and 37. It is to be noted that the variouscomponent parts 31 to 37 altogether constitute a difference amplifier 30and an output side of the difference amplifier 30 is connected with aninput side of the voltage controlled oscillator 40.

Furthermore, an output EAO of the difference amplifier 30 is appliedwith an oscillation frequency initializing means, and an output signal Sfrom the oscillation frequency initializing means 70 is inputted to thecomparator 27 and the driving transistor interrupting circuit 80. Anoutput side of the driving transistor interrupting circuit is connectedso that signals Su, Sv and Sw outputted from the driving transistorinterrupting circuit 80 can be inputted to the respective bases of thedriving transistors 13, 14 and 15, respectively.

The operation of the drive device for the brushless motor so constructedas hereinabove will be hereinafter described.

In FIG. 1, the output from the voltage controlled oscillator 40 istransmitted to the driving coils 1 to 3 through the frequency divider41, the power supply switching signal generator 44 and the drivingtransistors 10 to 15. Accordingly, the output from the voltagecontrolled oscillator 40 and the power supply waveforms of the drivingcoils 1 to 3 have a predetermined phase relationship. In other words, bycontrolling the oscillation frequency and the phase of the voltagecontrolled oscillator, it is possible to control the difference in phasebetween a counterelectromotive force of the driving coils and the powersupply waveforms of the driving coils. In the event that a deviationoccurs in the phase angle between the counterelectromotive force of thedriving coils and the power supply waveforms of the driving coils, aphase difference ψ thereof is detected and amplified by the phasedifference detector 20 and the difference amplifier 30 and, by providinga phase control loop for controlling the oscillation frequency and thephase of the voltage controlled oscillator 40 so as to render the phasedifference ψ to be zero, it is possible to secure a proper power supplycondition to the driving coils. Accordingly, it is possible to stablyand efficiently generate a motor driving torque at all times and themotor can be driven.

The operation of the phase difference detector 20 will now be described.The driving coil 1 is supplied with signals U1 and U2 (that is, signalsU_(H) and U_(L)), synchronized with D1 and D2 which are frequencydivided outputs of the voltage controlled oscillator 40, as a powersupply command signal. Accordingly, the period during which both of thesignals U1 and U2 are not outputted is a power supply interruptingperiod and, during this period, the power supply waveform Uo of thedriving coil coincides with a counterelectromotive force Ue. The powersupply interrupting period is a period starting from the timing at whichthe signal U1 is rendered to be Low and ending with the timing at whichthe signal U2 is rendered to be High and corresponds to one clock of thesignal D1 or four clocks of the signal D2. Although a similar powersupply interrupting period exists even during the period subsequent tothe signal U2 being rendered to be Low and prior to the signal U1 beingrendered to be High, only the former period is taken into considerationfor the sake of brevity. During the power supply interrupting period,comparing a neutral point voltage No of the driving coils with the powersupply waveform Uo of the driving coil, when the phase difference ψbetween the power supply waveform Uo and the counterelectromotive forceUe of the driving coil is zero, the neutral point voltage No and thepower supply waveform Uo coincide at a timing intermediate of the powersupply interrupting period, that is, a timing after 2 clocks of thesignal D2 subsequent to the signal U1 being rendered to be Low. Also,where Uo is delayed relative to Ue by a phase difference ψ, No and Uocoincide before the timing 2 clocks of D2 prior to U1 being rendered tobe Low, and, where Uo is advanced relative to Ue by a phase differenceψ, No and Uo coincide after the timing 2 clocks of D2 subsequent to U1rendered to be Low. Accordingly, by comparing Uo and No with each otherafter 2 clocks of D2 subsequent to U1 being rendered to be Low, one canknow the phase relationship between Uo and Ue. Therefore, if as a methodof detecting the phase difference ψ arrangement is made to generate aphase difference detection pulse signal S having an appropriate width inreference to the timing 2 clocks of D2 subsequent to U1 being renderedto be Low and to compare No and Uo with each other only at the time thesignal S is generated, the comparator output PD having a dutycorresponding to the phase difference ψ can be obtained.

While in the foregoing the principle of operation has been made inconnection with the detection of the phase difference ψ in which thepower supply interrupting period subsequent to U1 rendered to be Low andprior to U2 rendered to be High with respect to the power supplywaveform Uo of the driving coil, a similar detection is possibleutilizing the other power supply interrupting periods relative to Uo,that is, the period subsequent to U2 rendered to be Low and prior to U1rendered to be high, and also, with respect to the power supplywaveforms Vo and Wo of the other driving coils 2 and 3, and in theillustrated embodiment the phase difference detector output PD isobtained by synthesizing all of them.

FIG. 2 is an explanatory diagram used to explain the operation ofFIG. 1. Immediately after the application of the power source voltageVcc, the output EAO of the difference amplifier 30 is generally unstabledepending on the initial charge accumulated in the capacitors 34 and 35and the state of the output PD of the phase difference detector 20.Accordingly, the output oscillation frequency f of the voltagecontrolled oscillator 40 is also unstable. Assuming that f is oscillatedat a very high frequency, the sequential power supply switching of thedriving coils 1 to 3 takes place at a high speed and the speed ofrotation of a rotating magnetic field is accelerated. On the other hand,since a movable element has an inertia, and if the speed of rotation ofthe rotating magnetic field is high immediately after the powering on,the number of revolutions of the motor will not follow the rotatingmagnetic field and will be unable to be started due to a loss of astarting torque. Therefore, in order to avoid the occurrence of thiscondition, an arrangement has been made in which the output S of theoscillation frequency initializing means 70 will be rendered to be of aHigh level immediately after the application of Vcc, causing EAO to belowered to thereby to render the oscillation frequency f to be a lowfrequency. When the movable element is lowered down to fmin at which itcan sufficiently follow the speed of rotation of the rotating magneticfield, the output S of the oscillation frequency initializing means isrendered to be of a Low level.

However, during a period in which the oscillation frequency initializingmeans 70 is operated, the movable element is generally in a constrainedcondition and an excessive electric current is flowing across thedriving transistor. Therefore, a heat loss of the driving transistors isincreased and an unnecessary electric power is supplied to the motor. Inview of this, in order to avoid the occurrence of this condition, all ofthe outputs Su, Sv and Sw of the driving transistor interrupting circuit80 are rendered to be Low when the output S of the oscillation frequencyinitializing means 70 is rendered to be of High level, therebyinterrupting the supply of an electric power to the bases of the drivingtransistors 13, 14 and 15 so that the supply of the electric power tothe driving coils 1, 2 and 3 can be interrupted. When the output S ofthe oscillation frequency initializing means 70 is rendered to be of Lowlevel, the operation of the driving transistor interrupting circuit isreleased to permit the driving transistors to initiate a respectiveswitching operation consequent upon the increase of f to a value higherthan fmin and, in correspondence therewith, the rotating magnetic fieldcan be progressively accelerated from the speed at which the movableelement can follow, with the motor consequently started.

Also, if the movable element is, for example, momentarily constrainedduring a condition in which the motor is efficiently driven, both of theoscillation frequency initializing means 70 and the driving transistorinterrupting circuit 80 are caused to operate in the same manner asthose taking place immediately after the power has been turned on,thereby to initialize f to a low frequency again with the motorconsequently started.

FIG. 3 is an explanatory diagram showing the above described operation.

It shows respective operations of the various component parts when themovable element is constrained at a timing to in FIG. 3 with the numbern of revolution of the motor rendered to be zero. According to FIG. 3,it is shown that an abnormality in the oscillation frequency is detectedat the timing t1, the initialization of the oscillation frequency iscompleted at a timing t2, the driving transistor interrupting circuit isoperated during a period from the timing t1 to the timing t2, and themotor is restarted after the timing t2.

INDUSTRIAL APPLICABILITY

As hereinbefore fully described, the drive device comprises a phasecontrolled loop for controlling an output of a voltage controlledoscillator (40) by supplying an electric power to motor driving coils(1, 2, 3), detecting the difference in phase between the power supplywaveforms thereof and a counterelectromotive force of the motor drivingcoils during a power supply interrupting period with the use of a phasedifference detector (20) and inputting a detected phase differencesignal to the voltage controlled oscillator (40), an oscillationfrequency initializing means (70) and a driving transistor interruptingcircuit (80). Therefore, the present invention does not require the useof the filtering circuit hitherto required thereby making it possible toconsiderably reduce the use of the capacitors of high capacitance and iseffective to avoid any possible reduction in efficiency resulting from avoltage drop attributable to the spike noises contained in the powersupply waveform of the driving coil, the electric current supplied andthe driving coil impedance, a variation in power source voltage and loadand the armature reaction and, at the same time, to avoid the increaseof the heat loss of the driving transistors and the supply of theunnecessary electric power to the motor during the condition in whichthe movable element is momentarily constrained immediately after theapplication of the power source voltage Vcc or during the motor beingdriven.

Also, the provision of the drive device for the brushless motor capableof exhibiting an extremely excellent characteristic in that any possibledestruction resulting from the increased heat loss of the drivingtransistors during the constraining of the movable element for aprolonged length of time can be realized at low cost.

We claim:
 1. A drive device for a brushless motor which comprises aplurality of phases of motor driving coils, a plurality of drivingtransistors connected with the driving coils, a power supply switchingsignal generator for sequentially transmitting a power supply switchingsignal to the driving transistors for driving the driving coils, avoltage controlled oscillator for outputting a signal having anappropriate frequency to the power supply switching signal generator, aphase difference detector for detecting the difference in phase betweena counterelectromotive force, generated in the driving coils during theinterruption of the supply of an electric power to the driving coils,and the power supply switching signals, a difference amplifier foramplifying an output from the phase difference detector and forinputting it to the voltage controlled oscillator, an oscillationfrequency initializing means for initializing the oscillation frequencyof the voltage controlled oscillator, and a driving transistorinterrupting circuit for disabling the plural driving transistors andfor starting the sequential supply of an electric power to the drivingtransistors at the time the oscillation frequency is initialized.
 2. Thedrive device for the brushless motor as defined in claim 1, wherein thephase difference detector comprises a phase difference detection pulsegenerator operable to generate a pulse signal during an appropriateperiod in which the supply of an electric power to the motor drivingcoils is interrupted, and a comparator for comparing a terminal voltageof the driving coils with a reference voltage in dependence on an outputpulse signal of the phase difference detection pulse generator.
 3. Thedrive device for the brushless motor as defined in claim 1, wherein thephase difference detector comprises a phase difference detection pulsegenerator operable to generate a pulse signal during an appropriateperiod in which the supply of an electric power to the motor drivingcoils is interrupted, a buffer circuit provided at terminals of thedriving coils, and a comparator for comparing an output voltage from thebuffer circuits with a reference voltage in dependence on an outputpulse signal of the phase difference detection pulse generator.